1. Field of the Invention
The present invention relates to apparatus and processes for packaging microelectronic device. In particular, the present invention relates to a packaging technology that utilizes compression for achieving a BGA surface mount-type electrical connection between a microelectronic device and a carrier substrate.
2. State of the Art
A variety of techniques are known in the art for attaching microelectronic devices (such as microprocessors, circuit components, and the like) to carrier substrates (such as motherboards, expansion cards, and the like). These techniques may include direct surface mounting of the microelectronic device to the carrier substrate and socket mounting of the microelectronic device. Socket mounting may comprise a socket mounted on the carrier substrate wherein the microelectronic device is attached to the socket by pins protruding from the microelectronic device, or wherein the microelectronic device is pressed into the socket to achieve electrical continuity between a plurality of lands on the microelectronic device and a plurality of terminals on the socket. However, in low profile applications, such as laptop computers, the height of the attachment of the microelectronic device must be minimized. Thus, sockets are usually not utilized because the socket adds an unacceptable amount of height to the assembly. Thus, for low profile applications, direct surface mounting is generally used.
FIG. 5 illustrates an exemplary surface mounted land grid array 200 comprising a microelectronic device package 208 including a microelectronic device 202 attached to and in electrical contact with a first surface 206 of an interposer substrate 204. The attachment and electrical contact may be achieved through a plurality of small solder balls 212 extending between contacts 214 on the microelectronic device 202 and contacts 216 on the interposer substrate first surface 206. An underfill material 218 may be disposed between the microelectronic device 202 and the interposer substrate 204 to prevent contamination. Further, a thermal interface (shown as heat slug 222) for dissipation of heat generated by the microelectronic device 202 during operation may be attached thereto. The interposer substrate first surface contacts 216 are in discrete electrical contact with contacts 224 on a second surface 226 of the interposer substrate 204 through a plurality of conductive traces (not shown) extending through the interposer substrate 204.
The electrical contact of the microelectronic package 208 to a carrier substrate (such as a motherboard) 232 is achieved with a plurality of solder balls 234 which extend discretely between the interposer substrate second surface contacts 224 and contacts 236 on a first surface 238 of the carrier substrate 232. The solder balls 234 are reflowed (i.e., melted) which attaches the interposer substrate 204 to the carrier substrate 232. This form of electrical attachment is called a ball grid array (xe2x80x9cBGAxe2x80x9d) attachment. The carrier substrate 232 includes conductive traces therein and/or thereon (not shown) which form electrical pathways to connection the first surface contacts 236 with external components (not shown).
The microelectronic device 202 and the interposer substrate 204 may be supported by a support structure 242. The support structure 242 includes a frame 244, a backing plate 246, a thermal plate 248, and a plurality of retention devices (shown as bolts 252 and nuts 254). The backing plate 246 is placed adjacent a second surface 256 of the carrier substrate 232. The frame 244 is placed adjacent to the carrier substrate first surface 238 and at least partially surrounds the microelectronic package 208. The thermal plate 248 abuts the heat slug 222 and extends over the frame 244. The bolts 252 extend through the backing plate 246, the frame 244, and the thermal plate 248, and are retained by nuts 254 threaded thereon. The frame 244 not only acts to support the assembly, but also acts as a stop to prevent overtightening of the retention devices, which could damage the microelectronic device. The thermal plate 248 is generally thermally conductive to assist the heat slug 222 in removing heat generated by the operation of microelectronic device 202.
Although the surface mounted land grid array 200 shown in FIG. 4 achieves a low profile, the attachment of the microelectronic device package 208 to the carrier substrate 232 by reflowing of the solder balls 234 makes it difficult to remove the microelectronic device package 208 after attachment. This, in turn, makes it difficult to replace a defective microelectronic device (resulting in high rework costs) and makes it difficult for an end user or retailer to upgrade the microelectronic device.
Therefore, it would be advantageous to develop new apparatus and techniques to provide a low profile microelectronic device attachment which allows for easy removal of the microelectronic device.
The present invention relates to a packaging technology that achieves a BGA surface mount-type electrical connection between a first substrate and a second substrate by pressure on the BGA solder balls rather than by the reflow thereof. An embodiment of the present invention includes a microelectronic component assembly comprising a first substrate having at least one contact and a second substrate having at least one contact. At least one solder ball extends between the first substrate contact and the second substrate contact, wherein the solder ball is attached to the first substrate contact. A compression mechanism imparts pressure between the first substrate and the second substrate.